The purification and characterization of S-adenosylmethionine (AME) synthase (E.C.2.4.2.13) from yeast is currently in progress. We have been able to demonstrate the existence of two molecular species of AMe synthase which exhibit differences in chromatographic behavior and electrophoretic mobility. These two species of AMe synthase have identical molecular weight, approximately 110,000 when estimated by Sephadex G-150. Both forms of the enzyme catalyze the cleavage of inorganic tripolyphosphate. However, one molecular species does not require exogenous AMe for this enzyme bound tripolyphosphatase activity, whereas the tripolyphosphatase activity of the other species is totally dependent upon added AMe.